The invention relates to a vertical rotor mill, in particular a hammer mill or an impact grinding mill for milling granular materials by means of beater tools mounted on a rotating, vertically arranged rotor.
Various embodiments of hammer mills or impact grinding mills having the axes of rotation of the rotors arranged either vertically or horizontally are known. For example, German Utility Model DE-U 8,810,234 describes a hammer mill having a vertical drive shaft with the drive beneath it. Unexamined German Patent DE-OS 3,636,869 describes a beater arm mill having a beater arm rotor arranged so it can rotate about its vertical axis. The material to be milled is supplied by a feed mechanism arranged on the top side of the mill.
European Patent Application EP-A 556,645 discloses an impact grinding mill having a housing in which is arranged a vertical rotor equipped with beater tools, where at least one inlet opening for the material to be milled is provided above the beater tools on the top side of the housing. The beater tools are arranged in groups in the direction of the axis of rotation, with those of one group lying in the same axis perpendicular to the axis of rotation. At least the ends of the beater tools of the top group on the outer end radially are located less far toward the outside than those of at least one lower group.
The impact grinding mill is operated on ambient air. The housing of the impact grinding mill is made of a lower conical collecting part and an upper cylindrical mill housing part. The mill housing part in turn surrounds a milling space, a screen and a discharge area for fine particles.
Vibration-absorbing gaskets are provided between the two housing parts. To improve the vibration-absorbing effect, Swiss Patent CH-A 686,875 proposes that the top side of the mill housing part be designed in the form of a top part such that at least three vibration absorbing devices containing spring elements arranged in a uniform distribution around the outer periphery of the mill housing, and in addition, a flange on the mill housing part is flexibly connected to the top part. The height of the connection between the mill housing part and the top part is adjustable (air gap). The resulting air gap is sealed by a gasket.
Impact grinding mills with cup-shaped screens are also known, e.g., according to U.S. Pat. Nos. 3,169,711 and 4,243,180, where the end face of the screen is oriented vertically or horizontally. In both cases, it is complicated to mount and remove the screens, because a multitude of parts must be removed. With large hammer mills, the screen is heavy and has a large jacket wall height, so that it is difficult to being it above the rotor without tilting it. European Patent EP-B 525,362 proposes a device whereby mounting and dismantling of the screen should take place rapidly and safely. To do so, at least two holders which are distributed around the periphery of the screen can be displaced between two stops by means of a linear guidance of the screen. One stop is selected so that the cup-shaped screen can be removed from the screen by moving it past the mill, and the other stop is reached when the rotor is surrounded by the screen jacket and the outer edge of the screen jacket projects on a corresponding sealing surface. Access to the screen or changing the screen must be accomplished through a door in the mill housing, which is not only tedious and time-consuming but can also interfere with sanitation and safety from hazards.
Therefore, the object of this invention is to simplify access to the screen and to the screen and to the beater tools of a vertical rotor mill and to improve the operating properties and expand the range of use of such mills.
The bottom part of the housing of the vertical rotor mill is designed in the form of a cone that surrounds the screen and can be lowered. In the lowered condition, the screen can be displaced by analogy with European Patent EP-B 525,362. The screen basket itself is designed in one or more parts, and the screen plate is preferably designed with all screen holes the same. The screens themselves are perforated with a special pitch and direction (overlapping in the longitudinal direction), which improves milling.
To improve the vibration-absorbing effect and the sound-absorbing effect, the motor flange is arranged in or on absorber elements or an absorber cuff.
Assembly and disassembly of the screen and also an eventual cleaning are significantly simplified by measures which are seemingly simple when taken separately. At the same time, the operating reliability is increased by a new safety concept, namely, access to the rotor and beater tools is impossible in the operating state.